1. Field of the Invention
The present invention relates to a method used in a communication device in a wireless communication system, and more particularly, to a method of handling data transmission and reception in device to device communication in a wireless communication system.
2. Description of the Prior Art
In many communication systems, there are usually at least one kind of nodes serving for central control of radio resource and other kinds of nodes serving for user usage by means of connecting at least a serving node. In 3GPP LTE system of wireless communication system, for example, the mentioned nodes serving for central control are eNBs, relay nodes, radio remote heads (RRH), remote antennas, base stations, etc. Those nodes serving for user usage can be UEs, mobile stations, handsets, user devices, machine type devices (i.e. having capability of communicating with other devices without users), etc.
New direct communications between two user devices are different from conventional communication through eNB. This kind of device to device communication is new in wireless communication systems, and there is few information so far. Some similar but different behaviors could be found in Bluetooth and WiFi. However, for those skilled in the art should know these two systems are different from communication systems with central control, e.g. LTE, LTE-Advanced, WCDMA, HSPA, WiMAX, etc. Note that, in current wireless communication systems with central control, two communication devices (i.e. two UEs) use a proximity service direct communication mechanism for communication by means of user plane transmission using E-UTRA technology via a path not traversing any network node (i.e. an eNB). In a word, with the proximity service direct communication, a first UE can perform data transmission/reception to a second UE, wherein the first UE and the second UE are both proximity service direct communication enabled.
However, the applicant notice a problem associated to the proximity service direct communication. Consider a scenario that the first UE is configured proximity service direct communication to the second UE. The first UE has a RRC connection with a first eNB. The second UE has a RRC connection with the first eNB or a second eNB. It is not clear how to handle data transmission and reception between the first UE and the second UE if the proximity service direct communication is terminated e.g. due to reconfiguration or radio link failure.
Moreover, after RRC reconfiguration or radio link failure, the UE may perform Packet Data Convergence Protocol (PDCP) re-establishment. In addition, the UE shall reset the header compression protocol, apply the ciphering algorithm and key provided by upper layers during the PDCP re-establishment, set Next_PDCP_TX_SN and TX_HFN to 0 for an uplink data transfer procedure, and set Next_PDCP_RX_SN and RX_HFN to 0 for a downlink data transfer procedure. Furthermore, when the UE performs the PDCP re-establishment, for radio bearers that are mapped on RLC AM, the UE shall if the radio bearer is configured by upper layers to send a PDCP status report in the uplink, compile a status report after processing the PDCP data PDUs that are received from lower layers due to the re-establishment of the lower layers, and submit it to lower layers as the first PDCP PDU for the transmission.
Based on the abovementioned specification, the applicant has what ciphering algorithm and key, PDCP parameter setting, status report, and etc. in mind for data transmission and reception between the first UE and the second UE if the proximity service direct communication is terminated.